The present specification relates to displays. More particularly, the present specification relates to head up displays (HUDs).
Conventional HUDs are generally large, expensive and difficult to fit into small airplanes. Often, conventional HUDs rely on large lenses to form adequate field of view and viewing eye box. Compact HUDs are needed for tactical jets and other small aircraft where space is constrained in the cockpit. Substrate guided or waveguide HUDs have been proposed which use waveguide combiners to preserve eye box size while reducing lens size. U.S. Pat. No. 4,309,070 issued to St. Leger Searle and U.S. Pat. No. 4,711,512 issued to Upatnieks disclose substrate waveguide HUDS where the pupil of a collimating optical system is effectively expanded by the waveguide structure.
Modern cockpits are incorporating large area head down displays (LADs or LAHDDs). The LADs can provide panoramic views and large areas to the display information below the glare shield of the aircraft. However, such LADs do not provide HUD capabilities and require space in the cockpit that is required by conventional HUDs. HUDs which use waveguide combiners have a smaller size but can be susceptible to glare or sunspot imaging. The susceptibility is increased in glass cockpit environments, such as, those associated with tactical aircraft.
Accordingly, there is also a need for a HUD that is less susceptible to glare and/or sunspot imaging. There is also a need for a low profile HUD which is compatible with LADs and has acceptable display performance in environments subject to sunlight or other light. There is a need for a HUD that can fit within the cockpit of a tactical aircraft or other small aircraft when an LAD is provided in the aircraft and has glare mitigation. Further, there is a need for a compact HUD for use with an LAD. Further still, there is a need for a HUD having a waveguide combiner that is less susceptible to solar glare and sunspot imaging.